The proposed work will delineate the normal range of serum pepsinogen II (PG II) levels according to age and sex, determine the distribution of PG II levels in patients with peptic ulcer disease, various types of gastritis, renal failure, and in postoperative patients with and without recurrrent ulcer, and examine the possibilities that PG II levels are genetically controlled and that high levels are a subclinical marker of the ulcer diathesis in duodenal ulcer patients with normal pepsinogen I (PG I) levels. In each of the above studies, serum PG I levels will also be determined to study total pepsinogen levels and the ratio of PG I to PG II. Pepsin I (PN I) and pepsin II (PN II) levels will be determined in gastric juice from ulcer and non-ulcer subjects and correlated with proteolytic activity and acid output. In addition, we propose to characterize the minor pepsinogen phenotypes by crossed immunoelectrophoresis and to determine their possible correlation with peptic ulcer disease.